Posted on February 21, 2002 at 11:20 a.m.
BIRMINGHAM, AL — UAB (University of Alabama at Birmingham) researchers have created a systematic method that health professionals can use to help halt the spread of tuberculosis (TB), according to a paper to be published in the February 27 issue of the Journal of the American Medical Association (JAMA). The method identifies those individuals most likely to develop TB infection from contact with, or exposure to, a contagious person, allowing health workers to maximize resources for testing, treating and controlling TB.
The researchers have named six variables that identify those most at risk for contracting TB infection following exposure. Those who have been in contact with a TB case who tested positive in a sputum smear test or had lung damage sufficient to produce a cavity or hole visible in chest x-rays were at the highest risk. The risk of infection increases for every hour of contact with the confirmed TB case. In addition, men are at more risk than women, blacks at more risk than whites and adults over the age of 16 are at more risk than children.
“Local health departments perform what is called a contact investigation, in an effort to find all those who might have been in close contact with an individual diagnosed with TB,” says Dr. William C. Bailey, director of UAB’s Lung Health Center and principal investigator of the study. “For the first time, our research gives health workers a model to follow to devote their shrinking financial and staffing resources on those most likely to be infected.”
Health departments begin the contact investigation as soon as it is suspected that someone has TB. They attempt to identify all those who may have come into close contact with the infected individual. The numbers of such contacts can vary. In the 292 TB cases evaluated by UAB in this study, the number of contacts per case ranged from one to181.
“In an ideal situation, every person who came into contact with someone with TB would be tested to see if they had contracted the disease and treated accordingly,” says Bailey. “But if you have 181 people possibly exposed to a single TB case, you must make some judgments about which individuals to test first. Our results give health departments a basis for making those judgments.”
“Our findings indicate that persons exposed to a TB case with a positive sputum smear or cavitation on chest x-ray would be those individuals most important to investigate first,” says Lynn B. Gerald, Ph.D., MSPH, assistant professor in the UAB Lung Health Center. “As the individual’s time spent with the case increased, his or her risk of infection would also increase. Therefore we would first investigate those contacts who spent a significant amount of time with the TB case.”
A positive sputum (mucus and saliva coughed up from the lungs) smear occurs in about 48 percent of confirmed TB cases. Lung cavitation, seen in x-rays as a hole in the lung, occurs in over a quarter of all TB cases.
“Use of this model should allow public health workers to substantially reduce the number of contacts investigated and save valuable resources,” says Bailey. “Combined with the skill and experience of TB field workers, this model will bring us closer to our goal of TB elimination.”
Alabama had a TB incidence rate of 5.2 per 100,000 people in 2001, one of the higher rates in the country. The World Health Organization estimates that there are 8-10 million new cases of TB worldwide each year. This research was supported by a grant from the National Heart, Lung, and Blood Institute of the National Institutes of Health.